Postgres connector support

mapshader/io.py

@@ -8,7 +8,6 @@
 from os.path import expanduser
 
 
-
 def load_raster(file_path, xmin=None, ymin=None,
                 xmax=None, ymax=None, chunks=None,
                 layername='data'):
@@ -41,3 +40,53 @@ def load_raster(file_path, xmin=None, ymin=None,
 
 def load_vector(filepath: str):
     return gpd.read_file(filepath)
+
+
+def has_postgis():
+
+    from sqlalchemy.exc import OperationalError
+
+    try:
+        conn = get_postgis_connection()
+        conn.connect()
+        return True
+    except OperationalError:
+        return False
+
+
+def doesnt_have_postgis():
+    return not has_postgis()
+
+
+def get_postgis_connection():
+    from sqlalchemy import create_engine
+
+    database = environ.get('PGDATABASE', 'template_postgis')
+    host = environ.get('PGHOST', '127.0.0.1')
+    port = environ.get('PGPORT', '5432')
+    user = environ.get('PGUSER', 'postgres')
+    password = environ.get('PGPASSWORD', '')
+
+    return create_engine(f"postgresql://{user}:{password}@{host}:{port}/{database}")
+
+
+def get_layer_from_postgis(layername, rows=None, where='1=1', geom_col='geometry'):
+
+    from sqlalchemy import text as normalize_sql
+
+    conn = get_postgis_connection()
+
+    sql = f'SELECT * FROM {layername}'
+
+    if where:
+        sql += f' WHERE {normalize_sql(where)}'
+
+    if rows:
+        sql += f' LIMIT {rows}'
+
+    sql += ';'
+
+    df = gpd.GeoDataFrame.from_postgis(sql,
+                                       conn,
+                                       geom_col=geom_col)
+    return df